The present invention relates to resin compositions containing inorganic finely divided powders which are improved in hue. Films produced by forming the compositions of the present invention are useful particularly as printing films requiring excellent hue.
It is known that a film exhibiting excellent printability and writability can be obtained by forming a composition comprising an olefin-based resin having blended therein an inorganic finely divided powder, such as calcium carbonate powder, into a film and by stretching the film (Japanese Patent Application Publication Nos. 46-4678 (1971), 46-34896 (1971), 46-40794 (1971) and 48-3902 (1973)).
As the inorganic finely divided powder of this type, calcium carbonate powders which are inexpensive, exhibit a high degree of whiteness and are stably available are preferably used. However, it has been found that in the case where the olefin-based resin composition contains, in addition to the calcium carbonate powders, other additives such as antioxidants, ultraviolet light absorbers, dispersing agents and lubricants, films formed from such a composition are changed to yellow or red in color when exposed to heat or noxious gases, which results in a substantial reduction in the value of the film.
For example, polypropylene-based compositions containing therein calcium carbonate as an inorganic finely divided powder and a mixture of "Topanol CA" [trade name, tris(2-methyl-4-hydroxy-5-t-butylphenyl)-butane, manufactured by ICI Co.] and "Ionox 330" [trade name, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, manufactured by Shell Chemical Co.] as an antioxidant result in films which are yellowed when they are exposed to heat or allowed to stand at room temperature for a long period of time.
Also, if titanium dioxide, known as an extender pigment, is blended into the above mentioned polypropylene-based composition in order to increase the whiteness of the film resulting therefrom, the resulting film tends to become yellow to a greater extent.
We have carried out various studies to find antioxidants and dispersing agents which are effective for preventing the yellowing and reddening of a film resulting from an olefin-based composition having mixed therein calcium carbonate as an inorganic finely divided powder when they are added to the composition. As a result, we have found that only when a combination of two or more specific phenolic antioxidants and a phosphorus antioxidant and a specific fatty acid as a dispersing agent are used, the yellowing and reddening of the resulting film can be effectively prevented. This invention is based on this discovery.